Cracking process



A ril 21, 1970 c. E. HEMMINGER CRACKING PROCESS Filed Jan.

3 Sheets-Sheet 1 Inventor C. E. HEMMINGER Patent Attorney United States Patent 3,507,777 CRACKING PROCESS Charles E. Hemminger, Westfield, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Jan. 25, 1968, Ser. No. 700,486 Int. Cl. Cg 29/20, 37/02 US. Cl. 208-86 3 Claims ABSTRACT OF THE DISCLOSURE This disclosure relates to a process for cracking petroleum fractions which have been obtained by solvent treatment of petroleum residuum at super-critical separation conditions.

In the catalytic cracking of petroleum fractions a balance must be maintained between the end point of the feed and catalyst life. On the one hand there is the desire to convert a maximum amount of cracking feed to the lighter, more valuable products and on the other hand there is the desire to maintain high catalyst activity over the longest possible period.

The two most significant properties of cracking feeds which affect the cracking catalyst are metals content and carbon content i.e. Conradson carbon. The adverse effect of nickel, vanadium, iron, copper and other metallic contaminants found in petroleum fractions boiling above about 900 F. upon catalysts used in catalytic cracking and hydroeracking has long been recognized. In continuous cracking operations very small concentrations of such contaminants in the feed lead to rapid poisoning of the catalyst, causing reduced yield, shift in product distribution, increased gas and coke make, shortened catalyst life and more frequent regeneration.

In a similar manner, an increase in the Conradson carbon of the cracking feed leads to a corresponding increase in the quantity of coke laid down on the catalyst. This reduces catalyst activity and the reduction in activity must be countered by increasing cracking temperature or by more frequent regenerations or by other means which lead to other adverse effects.

The most common means of avoiding the effects of metals and carbon on cracking reactions is to set the cut point of distillation so that the metals content and the Conradson carbon of the feed are very low. Yet in the case of catalytic cracking every additional barrel of material that can be cracked has a value of about $1.50 more that the value of the same barrel as fuel oil.

Any means which will increase the end point of cat cracking or hydrocracking feed is of interest. In the past deep cut vacuum distillation, vis-breaking, heat soaking, solvent deasphalting and many other pretreatments have been proposed, however none of these seem to have gained wide acceptance.

The object of this invention is to provide a pretreatment means which will permit an increase in the end point of cracking feeds and subsequent cracking without an increase in the metals and carbon level laid down on the catalyst in continuous operations. Briefly summarizing the process comprises solvent treatment of the feed at supercritical conditions followed by catalytic cracking, hydrocracking, or both. In addition, a very important embodiment of the invention comprises treatment of certain cycle streams in the process.

Further details and advantages of the process are described below with reference to the drawings in which FIGURE 1 is a fiow sheet illustrating a catalytic cracking embodiment, FIGURE 2 is a flow sheet illustrating an embodiment including both cat cracking and hydrocracklit) 3,507,777 Patented Apr. 21, 1970 ICC ing and FIGURE 3 is a flow sheet illustrating a hydrocracking embodiment.

The objective of the supercritical separation step of the process is to provide the maximum yield of light oil from which the compounds containing metals and the hydrocarbons having a high Conradson carbon have been excluded.

supercritical separation is a means of separating a mixture into component fractions employing as separating agent a relatively low molecular weight compound at supercritical temperature and pressure.

The separation of the fraction(s) is primarily by boiling point of the components and this is similar to distillation. In addition some influences of compound type are evident resulting in a separation effects like those of solvent extraction.

A requirement of supercritical separation is that at least two phases must be formed by the solvent-feed mixture. If the properties of the feed are too similar to those of the solvent the mutual solubility of the two will be SO great that the formation of two phases will require an inordinate quantity of solvent or carrier gas relative to the quantity of oil feed. Generally it is preferred that the initial boiling point of the feed should be about 200 F. above the critical temperature of the solvent.

The mode of operation of supercritical separation and the processing equipment used are similar to those used in solvent extraction. In one embodiment, the solvent or carrier gas is mixed with the fraction to be separated at supercritical conditions and two phases are formed. The phases are allowed to separate in a settler. In a preferred embodiment shown in the drawings of this disclosure the feed and solvent are passed through a tower at supercritical conditions with refiux. A light phase is recovered overhead and a heavy phase is recovered as bottoms from the tower. The solvent is recovered from the separated fractions and recycled.

The most important operating variable in supercritical separation is temperature. It is necessary to operate at a temperature significantly above the critical temperature of the solvent in order to obtain the improved selectivity characteristic of this process. This operating temperature shall sometimes hereinafter be referred to as CT+, i.e. critical temperature plus. For any particular feed and solvent there is a narrow optimum CT+ range which will provide the desired enhanced selectivity. If the operating temperature is below the optimum range, selectivity is not improved. If the temperature is above the optimum range, the yield of the light phase is decreased.

Pressure is also an important operating variable. The capacity of a solvent or a carrier gas to extract a light oil phase from an oil feed is essentially nil at pressures near the critical pressure of the solvent. This capacity increases with increasing pressure. This operating pressure shall sometimes hereinafter be referred to as CP+, i.e. critical pressure plus. The optimum upper limit of operating pres-.

sure is not so sensitive or narrow in terms of decline in selectivity as it is in the case of the upper temperature limitation. Instead, equipment limitations such as wall thickness of reactors, separators and piping affect the selection of operating pressure.

The light phase taken overhead from the supercritical separation zone comprises a mixture of solvent and light oil at supercritical conditions. The oil can be recovered from the solvent by either increasing the temperature or by decreasing the pressure on the light phase. If desired, the light phase can be divided into a multiplicity of fractions by stagewise alteration of temperature or pressure. This separation is by boiling point with the heaviest or least volatile materials being removed in the first stage while successively lighter fractions are obtained in the subsequent stages.

The optimum operating conditions for the supercritical separation step are obtained as follows:

(1) The feed is studied in conjunction with the desired result. For example, in the case of preparing feed for catalytic cracking a prime feed would boil in the range of about 500-1000 F. and contain less than 2 p.p.m. metals (nickel equivalent). The Conradson carbon should be below 1.0 wt. percent.

(2) A suitable solvent is selected having a critical temperature of about 200 F. less than that of the feedstock. In this case propane or a propane-butane mixture would be satisfactory.

(3) A eries of autoclave runs are made to determine the optimum separation temperature, pressure and solvent to oil ratio. The autoclave is charged with oil and heated to a selected supercritical temperature. The system is pressured to a suitable supercritical pressure. A light solventoil phase is expanded to atmospheric pressure through a back pressure regulator. The gaseous solvent is metered through a wet test meter. The solubility of oil in the solvent is determined from the product volume and wet test meter readings. Any desired number of runs can be made to obtain the conditions necessary for eliminating metals and coke formers from the cat cracking feed.

Referring to FIGURE 1, a suitable feed from which a cat cracking feed can be separated is passed by line 1 through pump 2 into the first supercritical separation unit 3. Suitable feedstocks include topped petroleum crude oils, atmospheric residuums. In addition, partially refined fractions such as coker distillates, thermally cracked fractions, wide cut heavy gas oils and other petroleum fractions can be included in varying amounts. Since one object of the pretreatment is to reduce the metals content of the feed to less than 10 p.p.m., preferably less than 2 p.p.m. equivalent nickel it is desirable that the material in line 1 contain less than about 200 p.p.m. metals equivalent nickel. In the case of high metals feeds it may be necessary to accept a lower yield from supercritical separation so that a low metals cracking feed is assured.

In their poisoning effect on catalysts all metals are not the same. A cracking feed could contain 1 p.p.m. nickel and about 8 p.p.m. vanadium since the latter has only about one-eighth the effect of nickel. This feed would be said to contain 2 p.p.m. equivalent nickel. Iron, copper and other metals also have an arbitrarily assigned equivalence to nickel. The feed may be preheated to any desired temperature.

The supercritical solvent is passed by line 4 into line 1 to mix with the feed. The solvent, sometimes hereinafter referred to as the carrier gas is preferably propane in this particular embodiment. In general any inert solvent having a suitable critical temperature and pressure can be used. A preferred group of solvents are the light aliphatic hydrocarbons containing 2 to 8 carbon atoms in the molecule. Critical properties of some of the light hydrocarbons are set forth below in Table I.

TABLE I Critical ressure Hydrocarbon Critlcal temp. F.) p.s.i.a.)

Ethane 93 750 212 690 304 555 387 495 Hexane 455 450 suitable for the solvents mentioned previously are set forth below in Table II.

TABLE II.-SUPERCRITICAL SEPARATION CONDITIONS 1 Propane.

In a continuous manner, a light phase comprising solvent and oil is recovered overhead by line 5 and a heavy phase, containing a minor amount of solvent, is recovered as bottoms by line 6. Pressure reduction and cooling are effected by valve 7 and cooler 8 and asphalt is recovered as a product. The solvent can be recovered for reuse in the process by means not shown. In part, control of the supercritical separation step and the quality of the cracking feed, is maintained by heating means 9. The heating means may be any suitable device, internal or external to the tower which heats the material passing through the top section of the tower. In this way a reflux action is achieved. Valve 10 in line 5 maintains separation pressure at the desired level. Pressure and temperature reduction on the light phase is accomplished by valve 10 and cooler 11. From separator 12 the solvent passes overhead as a gas through line 13. The gas is cooled in cooler 14 and pumped by pump 15 and lines 4 and 1 back into tower 3. The light phase oil is removed from separator 12 by line 16 and passed through pressure reduction valve 17 and heater 18 into flash tower 19. From the flash tower a small residue of solvent is removed overhead by line 20 through cooler 21 and pump 22 for recycle via lines 4 and 1. Cat cracking feed is passed by line 23 to cracking unit 24.

The superiority of supercritical separation over vacuum distillation and conventional deasphalting is illustrated below on a fraction of light Arabian crude oil on which a comparison was made.

It can be observed that separation at supercritical conditions provided a cracking stock containing only 0.2 p.p.m. metals and a Conradson carbon of 1.5. Furthermore 20% less oil was rejected as bottoms for use as low price fuel oil.

Cracking in reactor 24 is carried out at conventional conditions with known cracking catalysts. Typical conditions are set forth below.

TABLE IV.CATALYTIC CRACKING CONDITIONS Broad range Preferred range Temperature, F 500-1, 200 750-1, 000 Pressure, p.s.i.g 0-500 0-50 LHSV, v./v./hr 2-200 5-100 Suitable catalysts include silica, silica-alumina, clays, silica-magnesia and these catalysts mixed with l50% molecular sieves.

Cracker effluent is passed by line 25 to fractionator 26. From the fractionator, gas and light ends are removed by line 27; gasoline is removed by line 28-, middle distillates are removed by line 29. Cycle oil is recycled by line 30. The bottoms removed by line 31 comprises 3 to 12 vol. percent of the fresh feed. This material contains an appreciable quantity of high boiling aromatic hydrocarbons and small amounts of catalyst fines, on the order of 0.3 to 0.1 wt. percent.

The bottoms fraction is passed by line 31 through pump 32 and heater 33 into the second supercritical separator 34. This unit is operated at conditions similar to those used in supercritical separator number 1 (reference numeral 3). The solvent, propane, is passed by line 35 into line 31 for mixing with the bottoms fraction. Employing a CT+ of 250 to 350 F. and a CP+ of 1500 to 2000 p.s.i.g., the light phase is continuously recovered overhead by line 36. This phase is mixed with the feed to supercritical separator number 1 in line 1. Thus the components of the cat crackerbottoms that are low in coke formers are recovered for cracking. Furthermore a common solvent recovery system serves both supercitical separation units. A heavy phase containing coke formers, i.e. heavy refractory aromatic hydrocarbons and catalyst fines is removed from separator 34 by line 37. Following pressure reduction through valve 38 and cooling in cooler 39, a bottoms material is recovered for further processing. Heating means 40 in separator 34 is employed to provide reflux resulting in precise control of the quality of the oil recovered in the light phase from supercritical separator 34.

In the embodiment described above two supercritical separation units are employed to prevent contamination of the asphalt recovered from the first unit. If there is little or no carry over of catalyst fines from cracking unit 24, the second supercritical separation unit is eliminated and the bottoms from the cat cracker fractionator is passed directly by line 31 to line 1.

The poor quality of the bottoms fraction for catalytic cracking is illustrated in the following table comparing the total recycle oil in line 31, the treated recycle oil in The gas is cooled and compressed in units 112 and 113 for recycle to tower 102. Catalytic cracking feed is passed by line 114 to catalytic cracking reactor 115. In one embodiment all or part of the cracking feed is hydrofined by closing valve 116, opening valve 117, passing the feed to hydrofiner 118 by line 119 and recovering hydrofined material by line 120. Hydrogen is supplied by line 121 and is recovered from the oil by line 122. Hydrofining conditioner, technique and catalyst are conventional. For example, temperatures of 500-l000 F., pressures of 500-5000 p.s.i.g. and catalysts comprising a metal selected from the group consisting of cobalt, molybdenum, nickel and tungsten on a support such as alumina or silica-alumina can be employed.

Catalytic cracking conditions and catalysts employed in reactor 115 are similar to those mentioned previously for unit 24. Cracker efiluent is recovered by line 123 and passed to fractionation tower 124. A gas fraction is recovered by line 125. A gasoline fraction is recovered by line 126. A kerosene fraction is recovered by line 127. A hydrocracking feedstock is recovered by line 128 and a bottoms fraction is recovered by line 129. Bottoms in line 129 are passed to settler 130. From the settler, a clarified oil is recycled by lines 131 and 114 to the cracker. Settler bottoms containing coke formers and catalyst fines is passed by lines 132 and 104 to the supercritical separation tower.

The hydrocracking feed passed by line 128 to hydrocracking reactor 133 comprises a fraction boiling in the range .of 600 to 950 F. and having a very low sulfur and metals content and less than 1000 ppm. nitrogen.

Conventional hydrocracking conditions, technique and catalysts are employed. Typical hydrocracking conditions are as follows:

TABLE VI.-HYD ROCRACKING CONDITIONS line 36 and the bottoms removed in line 37 from the SCS Bmad range Preferred unit No, 2, Temperature, F 550-950 660-800 Pressure, p.s.i.g sou-5, 000 1, 000-2, 000 TABLE V Space velocity, v./v./hr 0.3-5.0 0. 7-1. 5

Totirl Treateld B tt S H h d k 1 d r y recyce 0 0m uita e y rocrac ing cata ysts comprise any esired 1 L 36 L 37 (Lme3 me me combination of a metal selected from the group cons1st- Paraffins, tp t 3M 10 ing of oxides and sulfides of cobalt, nickel or the corre- Naphthenes 67. 3 68. 0 64 l Aromatics 2,3 spondmg free metals, platinum and pal adium distended on a solid cracking base such as silica alumina, silica- FIGURE 2 discloses an embodiment of the invention in which a single supercritical separation unit is used to provide three functions. First, the metals and Conradson carbon content of the feed is reduced to an acceptable level. Second, coke formers and catalyst fines are removed from the cat cracker bottoms fraction. Third, complex heavy aromatics such as coronenes and ovalenes are removed from hydrocracker bottoms.

Referring to the flow sheet, a feed like that of FIG- URE 1 is passed by line 101 to supercritical separation unit 102. A solvent such as propane is recycled by line 103 for mixing with the feed in. line 101. Recycle streams from line 104 are also mixed with the feed. The CT+ temperature and CP+ pressure in unit 102 are similar to those of the supercritical separators of FIGURE 1. In one embodiment a wash oil is fed into the top of tower-102 by line 105. A suitable wash oil comprises a fraction of cycle stock recovered from catalytic cracking boiling in the range of 800-1100 F. preferably 900- 1050 F. The wash oil can be clarified oil-a Eat. cycle stock from which tar and catalyst fines have-been removed. A heavy bottoms fraction is removedfrom tower 102 by line 106 and recovered after passing through pressure reduction valve 107 and cooler 108. Solvent and wash oil can be recovered from the bottoms fraction by conventional means, not shown.

The light phase comprising solvent and the desired catalytic cracking feed is recovered overhead from the tower by line 109 and passed to separator 110. From the separator propane is recovered overhead by line 111.

magnesia, silica zirconia, acid treated clays and the like. The most preferred type of hydrocracking catalyst is based on zeolitic, crystalline, aluminosilicate molecular sieves having relatively uniform pore diameters of about 6-14 angstroms. The sieves are composited with Group VIII hydrogenating metals and promoted with rare earths, if desired.

Hydrogen is supplied by line 134. Hydrocracker efiluent is passed by line 135 to fractionation tower 136. Hydrogen is recovered by line 137 and passed to separator 1 38 in which impurities are separated and removed by line 139. Hydrogen is recycled by lines 140 and 134. A light fraction (C -190 F.) is recovered by line 141. A 190350 P. fraction is recovered by line 142. A 350- 450 P. fraction is recovered by line 143. A bottoms fraction boiling above 450 F. is recovered by line 144. This latter fraction is passed to separator 145.

Hydrocracking of distillate fractions is designed to be an extinction recycle type of operation. Certain difficulties are created however by heavy hydrocarbons chiefly aromatics having more than three aromatic rings. Typical of these aromatics are coronene which has 6 interconnected rings and ovalene which has 10 rings.

These molecules are not cracked in the presence of molecular sieve catalysts because they will not enter the catalyst pores. Since they are continuously recycled around the unit, a build up occurs and this appears to cause vor contribute to catalyst deactivation rate and plugging of process units such as heat exchangers. Flash separator is used to control the endpoint of the 7 recycle in line 146 to a temperature Within the range of 600-950 F. to eliminate the build up of aromatic hydrocarbons having more than 3 rings in the molecule. The undesirable material is recycled to the supercritical extraction step by line 104.

The embodiment of FIGURE 2 thus provides an efiicient means of removing metals, coke formers and other undesirable materials from fresh and recycle streams fed to catalytic cracking and hydrocracking.

FIGURE 3 discloses an embodiment of the invention in which a petroleum residuum feed is prepared for hydrocracking and hydrocracked in a slurry type reactor. While distillate hydrocracking is a. successful commercial process, essentially no residuum hydrocracking process has found general acceptance. The principal reason is that catalysts which provide the required conversions are very rapidly deactivated by the metals and coke formers in the wide boiling range feed.

Referring to FIGURE 3, a petroleum residuum is fed by line 201 to the first supercritical separation unit designated by reference numeral 202. The feed is a residuum containing 30 l0% of materials boiling at more than 900 F. Stocks of this type are obtained from crude topping, atmospheric or vacuum distillation, visebreaking, heat soaking, thermal cracking, deasphalting, etc. The feed can be a blend of the residual material with distillate, straight run fractions and recycle fractions. The feed will contain -500 p.p.m. metals as nickel equivalent, 0.2 to 5.0 wt. percent sulfur and it will have a relatively high Conradson carbon content above about 2 to wt. percent. The object of this embodiment is to convert the feed into gasoline, low sulfur heating oil and low metals, low carbon cat cracking feed. The process can be operated to maximize any one of these hydrocracker fractions. Since the slurry reactor is designed to process a feed having a fairly high metals content and Conradson carbon it is only necessary to reduce the metals content to about -100 p.p.m. and the Conradson carbon to about 1 to 5 wt. percent.

A suitable solvent selected from those mentioned previously in this disclosure is recycled by line 203 for admixture with the feed. The supercritical extraction conditions including CT+, CP+, and solvent to oil ratio are selected from the ranges mentioned previously. A series of tests carried out as described herein can be used to chose the optimum supercritical conditions and solvent for a particular feed and a particular product spread. The asphalt phase is removed by line 203 for recovery of solvent and asphalt product. The light phase is passed overhead by line 204 to separator 205. Solvent is separated from the light phase oil for recycle via lines 206, 203, and 201. Suitable temperature, pressure, heat exchange and pumping conditions are maintained by known means in lines 204, 206 and 203 as well as in separator 205 to efiiciently recover and recycle the solvent. The light phase oil reduced in metals and coke formers is passed by line 207 to slurry hydrocracking reactor 208. Preferably the reactor is operated upflow and the oil is mixed in line 209 with recycle catalyst at the bottom of the reactor. Hydrogen is added to the oil by line 210. Suitable reaction conditions are chiefly dependent on the desired product spread and the amount of feed desulfurization wanted. Temperatures ranging from 650 to l800 F.; pressures ranging from 1000 to 5000 p.s.i.g.; hydrogen rates of 3000 to 9000 std. cu. ft. per bbl.; catalyst feed and rejection of 1 to 10 lb./bbl. of feed and space velocities of 0.2 to 2.0 w./w./hr. are used.

The reactor is operated so that the catalyst will be held in concentrated suspension in oil within the reactor so that the maximum utilization of the catalyst particles will be obtained before they are carried overhead in the effluent oil. The average residence time of catalyst can be on the order of 100 to 1000 hours. The size range of the catalyst is & to inch mesh and the particle density is 0.5 to 0.9 g./cc. Unreacted hydrogen is recovered by line 211, impurities are separated in separator 212 and the hydrogen together with make-up hydrogen from line 213 is recycled by line 210.

Cracking efiluent is passed by line 214 to fractionator 215. Light ends are recovered by line 216. Gasoline is recovered by line 217, heating oil is recovered by line 218 and gas oil suitable for catalytic cracking is recovered by line 219'. Considerable amounts of catalyst and small amounts of carbonaceous solid and ash collect in the bottom of separation unit 215 and these are passed by line 220 to the second supercritical separation unit designated by reference numeral 221. Solvent is passed to the unit by line 222. The light phase is removed overhead by line 223 and passed to separator 224. Solvent is recovered by line 225 for recycle by lines 203 and 222 and the light oil is passed by line 226 for mixing the feed in line 201.

A slurry of heavy oil and catalyst is removed from supercritical separator 221 by line 227 for recycle by lines 228 and 209 to reactor 208. A quantity of catalyst, ash and tar is removed from the system by line 229. Fresh make-up catalyst is added to the system from hopper 230 by line 231.

In another embodiment not shown hydrocracking is carried out in an ebbulating bed and a slurry of catalyst and oil is continuously removed directly from the reactor for supercritical separation.

The wash oil described with reference to supercritical separation unit 102 of FIGURE 2 can be used to advantage in unit 221 of FIGURE 3 to remove carbon and metals from the catalyst undergoing separation in the unit.

It should be understood that the foregoing detailed description and specific processing embodiments are given merely by way of illustration and many obvious alterations may be made therein without departing from the spirit of the invention.

I claim:

1. A process for the catalytic cracking of petroleum comprising the steps of continuously:

(1) Contacting the petroleum with an inert light hydrocarbon solvent containing 2-8 carbon atoms in the molecule at a CT+ of 550 F. above the critical temperature and a CP+ of 3001000 p.s.i.g. above the critical pressure in a first supercritical separation zone (2) Recovering a light extract phase comprising an oil fraction containing less than 2 p.p.m. metals and solvent (3) Recovering the major proportion of the solvent by releasing pressure on the said phase (4) Recovering the balance of the solvent from the extract oil by heating and flashing (5) Cracking the extract oil at a temperature in the range of 750-1000 F. in the presence of a silicaalumina cracking catalyst (6) Recovering a plurality of cracked fractions (7) Recovering a bottoms fraction containing catalyst fines and refractory aromatic hydrocarbons (8) Contacting said bottoms fraction in a second supercritical separation zone with a solvent having the same composition as the solvent employed in first supercritical separation zone (9) Recovering a light extract phase from the second supercritical separation zone (10) Passing said phase to the inlet of the first supercritical separation zone (11) And removing a bottoms phase containing catalys fines from the process.

2. A combination process comprising the steps of (1) Contacting a petroleum feed with an inert light hydrocarbon solvent at a temperature above the critical temperature and a pressure above the critical pressure in a supercritical separation zone (2) Recovering a light extract oil phase having a substantially reduced metals and Conradson carbon content (3) Separation solvent from said phase (4) Cracking the oil in the presence of a cracking catalyst (5) Recovering a hydrocracking feed from the effluent from the cracking step (6) Cracking said hydrocracking feed in the presence of hydrogen and a molecular sieve containing hydrocracking catalyst (7) Recovering a bottoms fraction containing coronenes and ovalenes (8) Separating an extinction recycle fraction from said bottoms fraction (9) And recycling the balance of said fraction containing the coronenes and ovalenes to the supercritical separation zone.

3. A combination process comprising the steps of continuously:

(1) Contacting a petroleum feed with an inert light hydrocarbon solvent at a temperature above the critical temperature and a pressure above the critical pressure in a first supercritical separation zone (2) Recovering a light extract oil phase having a substantially reduced metals and Conradson carbon content (3) Separation solvent from said phase (4) Hydrocracking the solvent free oil as a slurry of hydrocracking catalyst and oil in essentially the liquid phase at superatmospheric pressure and elevated temperature in the presence of added hydrogen (5) Withdrawing etfiuent including some of the catalyst from the hydrocracker (6) Fractionating the efiluent to obtain hydrocracked products (7) Withdrawing a heavy bottoms fraction from the fractionation zone containing metals and coked catalyst (8) Contacting said heavy bottoms fraction with an inert light hydrocarbon solvent at supercritical conditions in a second supercritical separation zone (9) Recovering a light extract oil phase for recycle [0 said first supercritical separation zone (10) Recovering a heavy bottoms phase comprising oil and catalyst (11) Recycling said phase to said slurry hydrocracking step (4).

References Cited UNITED STATES PATENTS 2,240,008 4/1941 Atwell 20886 2,391,576 12/ 1945 Katz et a1. 208366 2,391,607 12/ 1945 Whaley 208354 2,700,637 1/ 1955 Knox 20886 2,800,433 7/1957 Read 20886 2,925,374 271960 Gwin et a1. 20886 3,328,287 6/1967 Smilski et al 208--86 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 

